First off, I’m a professional mechanic for reference.
I installed a new XTR front brake on my XC bike and I still have a Magura MT7 on the rear.
I was riding it the other day and I just could not get great braking power out of it. I could lock up the rear Magura easily but the XTR would still move with a fist full of brake.
I know this won’t be as powerful as a Magura but I’m still shocked by this and wondering if it’s an install or contamination error or if my expectations are misaligned.
I am religious about avoiding contamination with my pads and rotors so before I replace those I wanted to check in to see if anyone has experience with these brakes.
the bleed is good. Lever hits resistance after just a short pull.
I did my regular in depth bed in process of 20 smooth braking to a near stop at a progressive level of speed. I also tried a hard but consistent drag on it on a downhill to really try to bed it in.
Which XTR brake is it? Enduro (M9220) or Race (M9200)?
Sounds like contamination. Had this issue with a leaking bleed port on a Magura MT8 rear brake. I could not lockup the wheel. Have you tried sanding the pads and cleaning the rotors with IPA and then immediately taking it for a test? Sometimes a cracked piston or damaged seal can be hard to see and feel.
Did you use a new rotor? If not, strip the Magura bedding off the old rotor with red scotch brite and re-bed with new pads or pads scuffed up with 320 grit wet/dry paper.
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I would do a quick sand of the pads and rotor and try doing the bed in again. Your bed in process is correct, but I find wetting the pads and rotor (squirting with a water bottle) before the bed in process creates a stronger transfer of pad material. Yes, the wet pads and rotors will howl during the process but they will be quiet again once they dry out.
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Yep, new XTR rotor with the new brake.
Yeah, sounds like a contaminated pad/rotor. 
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I’m going to try a new pad and rotor but it’s really annoying and expensive for all new brake parts so just wanted to see if this was a much weaker brake than I’m used to with my Maguras.